This video is taken from the varFDTD Learning Track on Ansys Innovation Courses.
We start with a blank MODE Solutions simulation file.
Add a rectangle from the Structures drop down menu for the substrate.
Edit the rectangle.
Set the x and y spans to 16 um, set z to -2 um, and the z span to 4 um.
Under the Material tab, set the material to "SiO2 (Glass) - Palik".
Next, add the ring resonator from the Object Library under the "Integrated optics" category.
Edit the structure group.
Set the position, set Lc which is the coupling length to 0, set the gap distance to 0.1 um,
set the ring radius to 3.1 um, set the material to "Si (Silicon) - Palik", set the base width
and height which is the width and height of the waveguides to 0.4 and 0.18 microns respectively,
set the x span to 14 microns, and base angle to 90 which means the waveguides will not
have sloped sidewalls.
Using the zoom extent button, you can zoom the view ports around the model.
Add the varFDTD solver region from the simulation drop down menu.
Edit the solver region and increase the simulation time to 5000 fs which is long enough for the
fields to fully propagate through this resonant device.
Under the Geometry tab set the x and y spans to 10 um, and the z span to 1 um.
Under the Effective index tab, we will use the default settings for the effective index
Set the simulation bandwidth to "broadband" since we are interested in the wavelength
range between 1.5-1.6 um and we want to include the effect of the material and waveguide dispersion
over this range.
There are settings here for the broadband material fit.
We will check the material fits later using the Material Explorer before running the simulation.
Next, we need to select the slab mode which is used to calculate the effective materials
which are used to collapse the 3D problem to a 2D problem.
The slab mode needs to be calculated for the vertical cross section of the structure including
the core material where the bulk of the power is contained.
In this case the silicon waveguide is the core material, so we need to set the slab
mode position to include the silicon.
You can enter the slab mode x and y coordinates here, but it is often easier to set the position
from the graphical view port.
Click "OK" to close the varFDTD edit window.
You can see a green cross in the XY view port which corresponds to the slab mode position.
You can click and drag the green cross and move it to a position where it overlaps with
the silicon waveguide.
You can also see 4 blue crosses which correspond to test point locations.
If I edit the varFDTD solver region again, the number of test points and positions of
the test points can be set from the Effective index tab.
The Material Explorer will show the calculated effective index for the slab mode as well
as at each of the test point locations.
The test points are only used to show the calculated effective index values at the specified
positions in the material explorer.
Their locations will not have any effect on the simulation results.
On the right-hand side of the Effective index tab, we can select the slab mode.
This can either be the "E mode" which is the fundamental mode where the electric field
polarization is in the XY plane, the "H mode", where the electric field is polarized along
the z-direction, or "user select" which can be used to select higher order slab modes.
We will use the "E mode".
You can plot the selected mode profile using the "plot current mode" button.
You can see that the fields are primarily contained in the silicon region which is between
z=0 and 0.18 um as expected.
We will use the default settings in the Mesh settings, Boundary conditions, and Advanced
Click "OK" to accept the settings.
Next, add a mode source from the Sources drop down menu.
Under the Geometry tab, set the geometry and position of the source so that it injects
from the straight waveguide at the top left of the device.
Under the Frequency/Wavelength tab, set the wavelength range to between 1.5-1.6 um.
In the General tab, we will use the default mode selection option of "fundamental mode".
Since the slab mode has been selected as the TE mode, the mode source will be injecting
the fundamental TE mode.
It's important to always make sure that the correct slab mode has been selected before
choosing the mode to inject.
Use the "Plot current mode" button to plot the field profile of the mode source along
The final step is to add monitors to record the transmission spectrum at the through and
Add a frequency domain field and power monitor from the Monitors drop down menu.
Edit the monitor and set the name to "drop".
In the Geometry tab set the monitor type to Linear Y, and set the position and span to
overlap the lower waveguide at the drop port.
Under the General tab, select "Override global monitor settings", and set the number of frequency
points to 500, and click "OK".
With the drop monitor selected, click the duplicate button on the left-hand side toolbar
to duplicate the monitor.
Edit the monitor and set the name to "through".
Under the Geometry tab, set the x position to 4.2 um and y to 3.6 um.
Add a frequency domain profile monitor from the Monitors drop down menu.
Set the name to "profile".
Set the x and y spans to 10 um and z to 0.
In the General tab, override the global monitor settings and set the number of frequency points
Now the simulation has been set up, and in the next unit we will run the simulation and
collect the results.